VMake allows to activate the built-in debugging features of the VLisp interpreter by using the command line option lispDebug. This provides support for new rules during development. In case of an evaluation error in LISP the interpreter stops an enter the standard break level to allow further investigation of the error. The break loop can be left by either the command (continue) for a continue able error or by typing the EOF character. If the interpreter seems to be in an endless loop, the evaluation can be breaked by sending the interpreter the signal SIGUSR1. In this case the break loop is entered similar to an error.
In interactive mode the command key 
may be
used either to evaluate directly a LISP expression or without any
parameter to enter the break level of the interpreter where all LISP
expressions can be evaluated.